Apparatus for detoxifying exhaust emissions of an internal-combustion engine

ABSTRACT

An antipollution device for detoxifying exhaust gases of an internal-combustion engine (i.e. a catalytic exhaust-gas reformer) has three nested coaxial tubes the inner two of which are perforated. The annular chamber between the inner tube and the intermediate tube is filled with a mass of catalyst kept in a packed condition by a spring-biased disk defining one end of the intermediate chamber. For this purpose the inner tube is conical and the intermediate tube can be cylindrical or conical. The outer chamber is filled with catalyst impregnated insulation and is provided with gas outlets while an entrance chamber communicates with the inner tube and is fed with raw exhaust gases from the engine through a feed chamber partially surrounding the outer tube. A burner is provided in the entrance chamber to heat up the catalyst during the first moments of engine operation to prevent fouling of this catalyst. The end of the apparatus may be removed for replacement of either of the inner two tubes, of the insulation, or of the catalyst.

Berger et al.

[451 Nov. 27, 1973 APPARATUS FOR DETOXIFYING EXHAUST EMISSIONS OF AN I INTERNAL-COMBUSTION ENGINE Inventors: Heinz Berger, Albaxer Str. 2,

Hoxter; Heinz-Werner Berger,

Drenker Str. 26b, Amelunxen, both of Germany Filed: Sept. 20, 1971 Appl. No.: 181,692

Foreign Application Priority Data Sept. 19, 1970 Germany P 20 46 324.5

US. Cl. 23/288 F, 60/284, 60/286, 60/290, 60/297, 60/300, 60/303, 60/307 Int. Cl. F0ln 3/14, BOlj 9/04 Field of Search... 23/288 F; SS/DIG. 30; 423/213, 214; 60/300, 303, 307

References Cited UNITED STATES PATENTS 10/1957 Bratton 23/288 F UX l/l962 Gerlich 23/288 F UX 7/1965 lnnes et al... 23/288 F 8/1965 Thomas 23/288 F X 10/1965 Ridgway... 23/288 F X 12/1965 Hettich et al. 23/288 F 5/1966 Morrell 23/288 F X 4/1968 Hamblin 23/288 F ENG/NE 3,503,716 3/1970 Berger I 23/288 F 3,581,490 6/1971 Morris 23/288 F X 3,649,213

3/1972 DePalma et al. 23/288 F Primary Examiner-Barry S. Richman Attorney-Karl F Ross [5 7] ABSTRACT An antipollution device for detoxifying exhaust gases of an internal-combustion engine (i.e. a catalytic exhaust-gas reformer) has three nested coaxial tubes the inner two of which are perforated. The annular chamber between the inner tube and the intermediate tube is filled with a mass of catalyst kept in a packed condition by a spring-biased disk defining one end of the intermediate chamber. For this purpose the inner tube is conical and the intermediate tube can be cylindrical or conical. The outer chamber is filled with catalyst impregnated insulation and is provided with gas outlets while an entrance chamber communicates with the inner tube and is fed with raw exhaust gases from the engine through a feed chamber partially surrounding the outer tube. A burner is provided in the entrance chamber to heat up the catalyst during the first moments of engine operation to prevent fouling of this catalyst. The end of the apparatus may be removed for replacement of either of the inner two tubes, of the insulation, or of the catalyst.

27 Claims, 6 Drawing Figures SHEET 2 OF 4 PAIENTEUNUY 27 I973 5:13 FIG. 6

Heinz Berger Heinz-Werner Berger INVENTORS.

PAIENIEDuuvNms 3,775,064

SHEET 3 OF 4 Heinz Berger Heinz- Werner Berger INVENTORS.

G A g'dRoss Attorney PATENTEDHUV 27 I975 SHEET t 0F 4 Mam/W Heinz Berger Heinz-Werner Berger INVENTORS.

hm Em o Zortz0- APPARATUS FOR DETOXIFYING EXHAUST EMISSIONS OF AN INTERNAL-COMBUSTION ENGINE FIELD OF THE INVENTION The present invention relates to an antipollution device for the waste gases of an internal-combustion engine and, more particularly to an antipollution device which is adapted to be used in a motor vehicle to detoxify and purify the exhaust gases thereof before they are released to the atmosphere, i.e. an exhaust gas catalytic afterburner or reformer.

BACKGROUND THE INVENTION .The internal-combustion engine presents a considerable pollution problem. Such engines produce considerable quantities of carbon monoxide, nitrogen oxides, assorted hydrocarbons, soot, and the like. Various carburetion systems as well as complicated electronic fuelinjection systems have been proposed, but the results have not been fully satisfactory as far as avoiding polluting exhaust fumes is concerned. Even though such systems work well much of the time, engines so equipped produce sizable amounts of pollution as soon as the timing fails to the slightest extent and, if one spark plug misfires frequently, the equipment is entirely useless.

Various catalytic systems have been tried in conjunction with the above-described arrangements, but again with little success since a change in the type of gas or a set of bad piston rings often leads to the coating of the catalyst, rendering it useless.

Afterburner systems have likewise been proposed to simply fully oxidize all of the polluting fractions in the waste gases. However, such arrangements have always produced a large amount of heat which could not be safely or efficiently dissipated.

OBJECTS OF THE PRESENT INVENTION It is therefore an object of the present invention to provide an improved antipollution apparatus.

Another object of this invention is the provision of an antipollution device which detoxifies completely the waste gases of an internal-combustion engine.

Another object is to provide a catalytic exhaust-gas reformer or afterburner which is simple, can be maintained with ease, is adaptable to various automobile structures and is highly efficient.

A further object is the provision of a compact wastegas oxidizer and filter which has a long service life and otherwise overcomes the disadvantages of the prior-art antipollution devices.

SUMMARY OF THE INVENTION The above objects are attained according to the present invention by an apparatus wherein three coaxial nested tubes are provided with the annular chamber between the inner and intermediate tubes filled with a catalyst in the form of a granulate, a metallic wool, small rings or wafers, disks, balls or the like, i.e. amobile catalyst mass. The chamber between the outer tube and the intermediate tube is vented to the atmosphere,

- and both the inner and intermediate tubes are preforated for radial gas passage through the chambers. An entrance chamber is provided at one end of the nested tubes and communicates with the interior of the inner tube while communicating with a feed chamber formed at least partly around the outer tube and connected to the engine exhaust. A burner is provided in this entrance chamber as well as a filter in order to preheat the catalyst in the intermediate chamber and to eliminate soot and water vapor from the waste gases prior to their contact with the catalyst.

Means are provided to operate the burner when the internal-combustion engine is started to preheat the catalyst and thereby prevent it from becoming coated with soot and the like. Similarly such a burner acts as a noncatalytic afterbumer to detoxify many of the normally toxic exhaust emissions, and, since it is directed axially into the inner tube, the heat it generates is dissipated throughout the entire apparatus. The device according to the invention can thus replace the usual muffler and serve as a muffler for sound damping purposes.

In accordance with another feature of this invention the catalyst is packed in the intermediate chamber by a spring-biased disk. To this end the inner tube at least is conical and shorter than the other two tubes so that the spring-biased disk can pack the catalytic bodies as, with time, the vibration of the vehicle, frictional abrasion and the like wear down or cause shrinkage of the catalyst bodies. Thus the formation of passages or channels in the catalyst mass, which can be traversed by unreformed exhaust gas, is precluded. The spring behind this disk is advantageously braced against a removable end cover to allow replacement and renewal of the catalyst. In'this manner no holes which would lead to through passage of poisonous gases form in the catalyst, and the back-pressure of the device remains substantially constant, positively influencing engine performance.

According to another feature of this invention the exhaust gases enter the entrance chamber through a filter grid and catalyst rim which catalytically reduce the nitrogen oxide before these waste gases are mixed with air at the burner. This grid simultaneously removes most of the condensates, carbon black, and lead oxides.

In accordance with further features of the invention a catalytic screen is provided in the outer chamber with an insulation body surrounding this screen to maintain high temperatures in the antipollution device for best working of the conventional platinum-base catalyst. This insulation body can in turn be impregnated with catalytic compounds. Such insulation maintains the temperature in the necessary infra-red range (580 620 C.) so that the catalysts will work at their most efficient level and their fouling is completely ruled out.

A blower is provided which can operate at least at two different speeds in order to insure a high air to exhaust-gas ratio in the apparatus. Means are provided to adjust the throughput of this blower according to engine speed and to the temperature within the antipollution device.

DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial section through an embodiment of the apparatus according to the present invention;

FIG. 2 is a cross section through the apparatus of FIG. 1;

FIG. 3 is an end view of the apparatus of FIG. 1;

FIGS. 4 and are schematic diagrams of control circuits for the apparatus according the the present invention; and

FIG. 6 is a detail view of an alternative embodiment of this invention.

SPECIFIC DESCRIPTION As seen in FIGS. 1 3 the apparatus of this invention has three coaxial nested tubes 1, 2 and 3 of heatand acid-resistant material, defining three chambers 4, 5 and 6. The inner tube 1 is conical and perforated along its entire length 1. The intermediate tube 2 is cylindrical and perforated only through the distance 1 in its regions surrounding this inner tube 1. Otherwise the intermediate tube 2 has a length L which is about onethird greater than 1. The outer tube 3 is provided with outlets 9 and is cylindrical. All three tubes 1, 2, and 3 are made of plated steel or another such heatand chemical-resistant material.

The conical chamber 4 within the inner tube 1 is empty of any solid structure while the intermediate chamber 5 between tubes 1 and 2 is filled with a packed mass of catalyst 8 in the form of a multiplicity of small catalytic bodies of round, cylindrical, or other shape. The mass of catalyst is not cohesive. A disk 17 seals the end of the chamber 5 and has a compression spring 18 which bears on a cap 19 threaded onto the end of tube 2. Another cap 33 seals the end of tube 3. As the catalyst 8 is reduced in size the spring 18 pushes the disk 17 to the right as seen in FIG. 1 to keep it densely packed. The degree of density of the catalyst is determined by the spring 18.

The intermediate tube 2 is formed with perforations 21 and is surrounded by a screen 22 in turn surrounded by a porous sleeve 23 of insulating material impregnated with a catalytic compound. This sleeve 23 has a length L" which is slightly longer than the perforated region 1 of the tube 2 and shorter than the overall length L of the chamber 5 as shown here before size reduction of the catalytic mass 8.

As best seen in FIG. 2 a U-section metal plate 11 defines a chamber overlying substantially half of the tube 3 and extending the full length thereof. Four exhaust-gas inlets 12 connected to an internalcombustion engine 34 are provided. The chamber 10 communicates through an orifice 10', a heated catalytic screen-filter 25 and a catalytic ring 24 with an entrance chamber 7 communicating in turn through a mixer 20 with the chamber 4.

An axial tube 13 extends through the ring 24 into the chamber 7 and is connected via conduit to a compressor 30 from which a second smaller-diameter conduit 26 feeds directly into the chamber 7. A nozzle 31 connected through a line 14 and an electromagnetically operable pressure-regulating valve 29 to a motorvehicle fuel pump 28 opens axially in the end of the tube 15 which is provided at its end with an atomizing screen 32. A spark plug 16 connected to an ignition coil 27 (see FIG. 3) is provided in the tube 13. Simultaneous operation of the pumps 30 and 28 along with opening of the valve 29 and firing of the spark plug 16 will cause a flame to form in the tube 13, directed to the left in FIG. 1.

Operation of the above-described apparatus will first be described with reference to FIG. 4 in which a twocycle engine 34 is used.

When the ignition switch 42 of the motor-vehicle is closed a relay 35 is operated to connect one side of the motor-vehicle battery 36 via contacts 35a through normally closed contacts 37a of a relay 37 to a transistorized tachometer-speed control 38 coupled to the ignition coil 45 of the engine 34 and also to connect the battery 36 via contacts 35b through a pair of normally open contacts 46a of a relay 46 to the coil 27. As the motor-vehicle starter button 40 is actuated a timed holding relay 41 is operated which in turn operates both of the relays 37 and 39. The contacts 41a and 41b of the relay 41 are designed to remain closed for 40 seconds, although up to seconds would be permissible.

Relay 39, on closing, breaks the circuit from the motor 30 through the tachometer 38 via contacts 39a and connects this motor 30 via contacts 39b directly through the contacts 35a of relay 35 and a 40-amp fuse to the battery 36. Since the normally-open contacts 39b of relay 39 are connected inward of resistors 43 connected between this motor 30 and the tachometer 38, and since the other side of the motor is connected only through a small resistor 44 to ground, the motor 30 operates at high speed delivering liters of air per minute to the chamber 7. For the same period relay 37 is closed so that its contacts 37a interrupt the connection between the tachometer 38 and the battery 36, and its contacts 37b and 370 connect the ignition coil 27 and the pump 28 and valve 29 to the battery 36. The normally closed contacts 46a of a relay 46 are connected across contacts 37a.

Finally once the engine 34 begins to run smoothly its generator 47 starts putting out sufficient current to open contacts 46a of relay 46. In this manner once the 40 seconds for the relay 41 are past, the coil 27, the pump 28, and the valve 29 are shut down, and the tachometer 38 takes over the feeding of current to the motor 30. At normal idle speed the motor 30 is operated by the speed-control tachometer 38 to have a throughput between 40.5 liters/minute (800 rpm) and 83.5 liters/minute (2400 rpm) depending on the rotation speed of the engine 34. The faster this engine 34 rotates, the faster the blower 30 is operated.

Thus, as the ignition is turned on the blower 30 starts to pass 40.5 liters/minute of air through the chambers 7, 4, 5 and 6, and thence out through outlets 9. When the starter switch 42 is actuated the blower is operated at a much higher rate and the burner is set into operation by sparking of the spark plug 16 and spraying of gas at the nozzle 31. Afier 40 seconds gas is no longer fed to the burner, and at the same time the speed of the blower 30 is reduced according to engine speed. Simultaneously or later, if the generator 47 is not yet operating sufficiently, the spark plug 16 is deactivated. These operations serve to heat up the catalysts 8 and 24 of the apparatus to between 580 and 620C., so that soot cannot deposit on the catalyst. In any case most soot, nitrous oxide, and the like is filtered out in the electrically heated filter 25, and the remaining carbon monoxide and hydrocarbons are oxidized in the chambers 7, 4, 5, and 6. Until the ignition switch 42 is opened again, the device functions completely without need of fuel.

FIG. 5 shows the schematic diagram for a four-cycle engine. When the ignition switch 42 is closed a relay 50 is operated and a pilot lamp 51 is lighted. This closes contacts 50a and 50b to start the motor 30 operating at its lowest speed, since it is connected in series across the battery with five resistors. 53 of equal resistance. Then actuation of the starter switch 40 operates a time relay 52 adapted to hold foronly 120 seconds, although up to 180. seconds would be permissible with a large en-' gine. Contacts 52a of the relay 52 thereby actuate a relay 54 whose contacts 54a and 54b feed current from the battery 36 to a point 55 in the circuit. The other normally open contacts 52b of the relay 52 connect a relay 56 to the point 55, closing contacts 56a of this relay. The above operationsfeed power to the coil 27, to the valve 29 to open it, to the pump 28, to a relay 57 having contacts 57a, and to a red pilot light 58. The relays 56 and 57 connect the motor 30 across the battery with only two of its five resistors 53, to operate this DC motor at top speed.

After 120 seconds relays '52, 54, and 56 are all deenergized as are the elements 27-29. Thus the burner stops, and the motor 30 is connected in series with at least three of its resistors 53. 1

Here the tachometer 38 includes a speed sensing circuit 59 which is connected to the spark coil 47 to actuate one of two relays 60 or 61, depending on engine rpm. On low engine rpm neither relay 60 nor 61 is actuated so that the contacts of relays 57 and 62 remain in the illustrated positions, with all five resistors 53 connected in series with the motor 30. On intermediate engine speeds the relay 61 is actuated to close the relay 62 and switch out one of the resistors 53, thereby speeding up the motor 30. On high engine rpm the other relay 57 which has a red pilot light 58 is also actu- FIG. 6 shows an alternative embodiment of the present invention wherein a conical tube 1' is formed of a plurality of segments urgedapart by springs- 1a, slits between the segments permitting gas passage. In I addition a conical tube 2 is provided so that the cross-- sectional area between them is-the same along their entire lengths. The springs la serve to tamp the catalyst 8. In addition a mixing orifice 20. is mounted on the tube 13 instead of on the wall separating the chambers 7 and 4. M

It should-be clear that the arrangement according to the present invention overcomes many of the disadvantages of the prior-art devices. It does not tend to foul up and become inoperative since its preheating maintains it at a high temperature where all soot and the like is burned. In addition it is easy to service since the catalyst 8, inner tube 1, intermediate tube 2, and spark plug 16 can all be quickly andeasily replaced without re-,

moving the unit from the car. In operation it uses the heat of the exhaust gases for catalytic reduction and afterburning.

We claim:

1. An antipollution apparatus for detoxifying the exhaust emissions of an internal-combustion engine, said apparatus comprising:

an outer tube provided with an outlet;

an intermediate tube within said outer tube'defining therewith an annular outer chamber;

a perforated inner tube within said intermediate tube and defining therewith an intermediate annular chamber, said intermediate tube being provided with throughgoing openings for gas passage between said intermediate and said outer chambers, said inner tube defining an inner chamber and being formed with throughgoing openings for gas passage between said inner and said intermediate chambers, said inner tube converging in one axial direction;

an entrance chamber communicating with said inner chamber;

a feed chamber on said outer tube and communicating with said entrance chamber, said feed chamber having an inlet adapted to be connected to an ex haustgas outlet of an intemal-combustion engine;

a gas-pervious mass of particulate catalyst in said intermediate chamber;

burner means in said entrance chamber for heating said catalyst by passing a hot gas therethrough; and

a spring-biased plate in said intermediate chamber bearing axially upon said mass in a direction opposite the direction of convergence of said inner tube.

2. The apparatus defined in claim 1, further comprising a gas mixer in said entrance chamber.

3. The apparatus defined in claim 2, wherein said burner means comprises an ignition tube extending into said entrance chamber and a spark plug in said ignition tube, said mixer being mounted on said ignition tube.

4. The apparatus defined in claim 1 wherein said inner tube is substantially conical.

5. The apparatus defined in claim 4 wherein said intermediate tube is substantially conical and said intermediate chamber is of substantially uniform crossssq n a ea- 77 77 7 7. ,7 77

6. An antipollution apparatus for detoxifying the exhaust emissions of an internal-combustion engine, said apparatus comprisingz 7 an outer tube provided with an outlet;

an intermediate tube within said outer tube defining therewith an annular outer chamber;

an inner tube within said intermediate tube and defining therewith an intermediate annular chamber, said intermediate tube being provided with throughgoing openings for gas passage between said intermediate and said outer chambers, said inner tube defining an inner chamber and being formed with throughgoing openings for gas passage between said inner and said intermediate chamhers;

an entrance chamber communicating with said inner chamber;

a feed chamber on said outer tube and communicating with said entrance chamber, said feed chamber having an inlet adapted to be connected to an exhaust-gas outlet of an intemal-combustion engine,

a gas-pervious catalyst in said intermediate chamber;

burner means in said entrance chamber for heating said catalyst by passing a hot gas therethrough, said inner tube being substantially conical and comprised of a plurality of conical segments, said apparatus further comprising a plurality of springs urging diametrically opposed ones of said segments apart.

7. The apparatus defined in ah arfiher ing an insulating sleeve in said outer chamber.

8. The apparatus defined in claim 6, wherein said inner, intermediate and outer tubes are constituted of a heatand chemical-resistant material.

9. The apparatus defined in claim 6, further comprising a spring-biased partition forming an end wall of said intermediate chamber.

10. The apparatus defined in claim 9, further comprising a removable end cap and a spring compressed between said cap and said partition.-

II. The apparatus defined in claim 6, further comprising a catalyst body in said entrance chamber in the communication path between said feed chamber and said entrance chamber.

12. The apparatus defined in claim 11, further comprising a filter on the side of said catalyst body turned toward said feed chamber.

13. The apparatus defined in claim 6 wherein said burner means includes:

an ignition tube extending into said entrance chamber;

a spark plug in said ignition tube;

means for feeding gas to said ignition tube; and

blower means for feeding air to said ignition tube upstream of said spark plug.

14. The apparatus defined in claim 13, further com prising conduit means for feeding air directly from said blower means to said entrance chamber around said tube.

15. An antipollution apparatus for detoxifying the exhaust emissions of an internal-combustion engine, said apparatus comprising:

an outer tube provided with an outlet;

an intermediate tube within said outer tube defining therewith an annular outer chamber;

an inner tube within said intermediate tube and defining therewith an intennediate annular chamber, said intermediate tube being provided with throughgoing openings for gas passage between said intermediate and said outer chambers, said inner tube defining an inner chamber and being formed with throughgoing openings for gas passage between said inner and said intermediate chambers;

an entrance chamber communicating with said inner chamber;

a feed chamber on said outer tube and communicating with said entrance chamber, said feed chamber having an inlet adapted to be connected to an exhaust-gas outlet of an internal-combustion engine;

a gas-pervious catalyst in said intermediate chamber;

burner means in said entrance chamber for heating said catalyst by passing a hot gas therethrough, an insulating sleeve in said outer chamber, said insulating sleeve being impregnated with a catalytically-active compound.

16. The apparatus defined in claim 15, further comprising a screen surrounded by said insulation sleeve.

17. The apparatus defined in claim 15, further comprising a gas mixer in said entrance chamber.

18. The apparatus defined in claim 15 wherein said inner, intermediate and outer tubes are constituted of a heatand chemical-resistant material.

19. The apparatus defined in claim 15, further comprising a spring-biased partition forming an end wall of said intermediate chamber.

20. The apparatus defined in claim 19, further comprising a removable end cap and a spring compressed between said cap and said partition.

21. The apparatus defined in claim 15, further comprising a catalyst body in said entrance chamber in the communication path between said feed chamber and said entrance chamber.

22. The apparatus defined in claim 21, further comprising a filter on the side of said catalyst body turned toward said feed chamber.

23. The apparatus defined in claim 15 wherein said burner means includes:

an ignition tube extending into said entrance chamher;

a spark plug in said ignition tube;

means for feeding gas to said ignition tube; and

blower means for feeding air to said ignition tube upstream of said spark plug.

24. The apparatus defined in claim 23, further comprising conduit means for feeding air directly from said blower means to said entrance chamber around said tube.

25. The apparatus defined in claim 15 wherein said inner tube is substantially conical.

26. The apparatus defined in claim 25 wherein said intermediate tube is substantially conical and said intermediate chamber is of substantially uniform crosssectional area.

27. The apparatus defined in claim 25 wherein said inner tube is comprised of a plurality of conical segments, said apparatus further comprising a plurality of springs urging said segments apart. u s a t 

2. The apparatus defined in claim 1, further comprising a gas mixer in said entrance chamber.
 3. The apparatus defined in claim 2, wherein said burner means comprises an ignition tube extending into said entrance chamber and a spark plug in said ignition tube, said mixer being mounted on said ignition tube.
 4. The apparatus defined in claim 1 wherein said inner tube is substantially conical.
 5. The apparatus defined in claim 4 wherein said intermediate tube is substantially conical and said intermediate chamber is of substantially uniform cross-sectional area.
 6. An antipollution apparatus for detoxifying the exhaust emissions of an internal-combustion engine, said apparatus comprising: an outer tube provided with an outlet; an intermediate tube within said outer tube defining therewith an annular outer chamber; an inner tube within said intermediate tube and defining therewith an intermediate annular chamber, said intermediate tube being provided with throughgoing openings for gas passage between said intermediate and said outer chambers, said inner tube defining an inner chamber and being formed with throughgoing openings for gas passage between said inner and said intermediate chambers; an entrance chamber communicating with said inner chamber; a feed chamber on said outer tube and communicating with said entrance chamber, said feed chamber having an inlet adapted to be connected to an exhaust-gas outlet of an internal-combustion engine; a gas-pervious catalyst in said intermediate chamber; burner means in said entrance chamber for heating said catalyst by passing a hot gas therethrough, said inner tube being substantially conical and comprised of a plurality of conical segments, said apparatus further comprising a plurality of springs urging diametrically opposed ones of said segments apart.
 7. The apparatus defined in claim 6, further comprising an insulating sleeve in said outer chamber.
 8. The apparatus defined in claim 6, wherein said inner, intermediate and outer tubes are constituted of a heat- and chemical-resistant material.
 9. The apparatus defined in claim 6, further comprising a spring-biased partition forming an end wall of said intermediate chamber.
 10. The apparatus defined in claim 9, further comprising a removable end cap and a spring compressed between said cap and said partition.
 11. The apparatus defined in claim 6, further comprising a catalyst body in said entrance chamber in the communication path between said feed chamber and said entrance chamber.
 12. The apparatus defined in claim 11, further comprising a filter on the side of said catalyst body turned toward said feed chamber.
 13. The apparatus defined in claim 6 wherein said burner means includes: an ignition tube extending into said entrance chamber; a spark plug in said ignition tube; means for feeding gas to said ignition tube; and blower means for feeding air to said ignition tube upstream of said spark plug.
 14. The apparatus defined in claim 13, further comprising conduit means for feeding air directly from said blower means to said entrance chamber around said tube.
 15. An antipollution apparatus for detoxifying the exhaust emissions of an internal-combustion engine, said apparatus comprising: an outer tube provided with an outlet; an intermediate tube within said outer tube defining therewith an annular outer chamber; an inner tube within said intermediate tube and defining therewith an intermediate annular chamber, said intermediate tube being provided with throughgoing openings for gas passage between said intermediate and said outer chambers, said inner tube defining an inner chamber and being formed with throughgoing openings for gas passage between said inner and said intermediate chambers; an entrance chamber communicating with said inner chamber; a feed chamber on said outer tube and communicating with said entrance chamber, said feed chaMber having an inlet adapted to be connected to an exhaust-gas outlet of an internal-combustion engine; a gas-pervious catalyst in said intermediate chamber; burner means in said entrance chamber for heating said catalyst by passing a hot gas therethrough, an insulating sleeve in said outer chamber, said insulating sleeve being impregnated with a catalytically-active compound.
 16. The apparatus defined in claim 15, further comprising a screen surrounded by said insulation sleeve.
 17. The apparatus defined in claim 15, further comprising a gas mixer in said entrance chamber.
 18. The apparatus defined in claim 15 wherein said inner, intermediate and outer tubes are constituted of a heat- and chemical-resistant material.
 19. The apparatus defined in claim 15, further comprising a spring-biased partition forming an end wall of said intermediate chamber.
 20. The apparatus defined in claim 19, further comprising a removable end cap and a spring compressed between said cap and said partition.
 21. The apparatus defined in claim 15, further comprising a catalyst body in said entrance chamber in the communication path between said feed chamber and said entrance chamber.
 22. The apparatus defined in claim 21, further comprising a filter on the side of said catalyst body turned toward said feed chamber.
 23. The apparatus defined in claim 15 wherein said burner means includes: an ignition tube extending into said entrance chamber; a spark plug in said ignition tube; means for feeding gas to said ignition tube; and blower means for feeding air to said ignition tube upstream of said spark plug.
 24. The apparatus defined in claim 23, further comprising conduit means for feeding air directly from said blower means to said entrance chamber around said tube.
 25. The apparatus defined in claim 15 wherein said inner tube is substantially conical.
 26. The apparatus defined in claim 25 wherein said intermediate tube is substantially conical and said intermediate chamber is of substantially uniform cross-sectional area.
 27. The apparatus defined in claim 25 wherein said inner tube is comprised of a plurality of conical segments, said apparatus further comprising a plurality of springs urging said segments apart. 